Preservation of rubber



Patented M725, 1948 PRESERVATION 01' some FrederlckEDownlngandOharleeJ-Pdeflm PennsGrove,N.J.,allignontoI.I.dnPont deNGIIIQIIHGFCGmMpWIIIIIIIIMMS corporation of Delaware No Drawing. Original application Sepimbfl' 2 1941, Serial No. 412,602. Divided and this application November 1, 1944, Serial No. 881,489

13 Claims.

This invention relates to the stabilization 01' organic substances and particularly to the stabilization of such substances which are subject to deterioration caused by the action of molecular oxygen and catalyzed by metals and their compounds.

Many organic substances, such as tats, edible oils, vegetable Juices, textile fibres, rubber, photographic developers and synthetic unsaturated compounds, are readily attacked by oxygen and the resulting deterioration, whether due to the accumulation of oxidation products or to secondary reactions induced by the primary oxidation products. imparts undesirable qualities to the substances and eventually destroys their usefulness.

The oxidation of these substances is promoted by: (1) autogenous catalysts formed by the oxidation of the substances themselves, and (2) extraneous catalysts which are accidentally present in the substances.

The autogenous catalysts, generally considered to be peroxides or monoxides, are responsible for the phenomenon termed auto-oxidation, wherein the reaction proceeds very slowly at first but gradually accelerates until a maximum is reached. The initial period of negligible reaction rate is called the induction period. Since these catalysts are integral constituents of the oxidative system, the particular process of oxidation cannot occur in their absence, and being derivatives of the substances, they are variable and possess different chemical properties.

0n the other hand, the extraneous catalysts, restricted in this case to copper, cobalt, iron and their compounds, do not occur of necessity in any organic substance which is not a derivative of these metals. Such metals may be present accidentally in any organic substance. The catalytic activity of these metals is inherent and is possessed by them in any medium unless the activity has been modified or suppressed by chemical means.

It has been found that certain compounds, known as antioxidants, retard the purely autocatalytic process, while some other compounds, herein named metal deactivators, suppress the catalytic activity of copper, cobalt, iron and their compounds. The nature and the action of antioxidants and metal deactivators will be described below, but without further discussion it may be concluded, from the facts presented above, that antioxidants must be specific with respect to the oxldizable organic substances and that deactivators must be specific for copper, cobalt and iron, and independent of the medium. Certain factors, however, such as reactivity or insclubllity, will determine whether a given deactivator can or cannot be used in a particular system.

years, in the preservation oi many or'ganic substances. by the discovery and use 01' compounds generically called "oxidation inhibitors" or antioxidant." These agents, mostly oxidizable organic compounds, retard the auto-catalytic process. Since antioxidants are themselves oxidized in the course of time. as a result oi auto-oxidation, the beneficial eflect obtained by their use is not permanent, and they protect the organic substances only so long as they are not rendered inactive. They are, moreover, very specific in action, each group of auto-oxldizable substances requiring a diiierent type 01' antioxidant for the best results.

Copper, cobalt, iron and their compounds accelerate the rate of oxidation oi many organic substances, including most or the antioxidants. Copper is generally the most potent. It is well known that these metals promote the formation of gum in gasoline, and speed up the aging of rubber and the development of rancidity in fats and oils. Hence these metals and antioxidants are antagonistic in action, and the normal inhibiting eflect of the latter is greatly reduced in the presence 0! the former.

Copper occurs naturally in many organic substances, but usually in such slight traces as to cause very little harm. The concentration of copper, however, is frequently raised during the course 01' handling and utilizing the substances. Vessels and conduits, made of metals containing copper, are used for storage and transportation. Ingredients, contaminated with copper, may be added. Copper may actually be required in one 0! the steps in the process for manuiacture, as in the copper sweetening oi gasoline.

It is an object 01 the present invention to retard the deterioration 01' organic substances caused by the action of molecular oxygen and catalyzed by the presence of catalysts, such as copper, cobalt, iron and their compounds. Another object is to render antioxidants, which are relatively ineflective in the presence oi. copper, cobalt, iron and their compounds, eflective to inhibit the oxidation of oxidizable organic substances even in the presence of copper, cobalt, iron and their compounds. A further object is to provide a new class of metal deactivators which are effective to render catalysts, such as copper, cobalt, iron and their compounds, inactive to catalyze the oxidation of oxidizable organic substances containing or in contact therewith. A still further object is to inhibit the deterioration of eiastomers, such as rubber, in the presence of copper, cobalt, iron and their compounds. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with our invention which Signal success has been achieved in recent o0 comprises adding to elastomers, such as rubber,

normally subject to deterioration caused by the action of molecular oxygen, and containing a catalyst of e group of copper, cobalt, iron and their compo nds, normally effective to catalyze oxidation of said elastomers, a small proportion of a metal deactivator sufiicient to deactivate the catalyst, such metal deactivator having the formula HRCH=N-R'OH wherein each of R and R represents an ortho divalent aromatic radical. The elastomers may also and generally will contain an antioxidant which is normally eifectlve to retard oxidation of the elastomer in the absence of the catalyst. We have found that such metal deactlvators will render the catalysts ineffective to catalyze the oxidation of the elastomer, including the antioxidant, when present.

Generally, in practice, the elastomer will also contain an antioxidant which is normally effective to materially retard the deterioration or oxidation of the elastomer in the absence of the catalytically active metals, but which is less effec tive in the presence of such metals.

Referring to the formula the term "ortho" means that the free valences belong to adjacent carbons of a benzene ring so that each of the hydroxy groups is ortho to the -CH=N- group. By the term arylene," we mean a divalent aromatic radical which consists of the elements carbon and hydrogen. By the term mononuclear radical of the benzene series," we mean that the radical contains only one benzene ring. While the radicals, represented by R and It, may contain a plurality of benzene rings as in diphenyl, naphthyl, anthracyl, phenanthryl and like compounds, we preferably employ those compounds wherein each of R and R represents an ortho divalent mononuclear aromatic radical of the benzene series. Also, while R. and B, may contain nonhydrocarbon substitutents, such as alkoxy, nitro, amino, hydroxy, aryloxy, halogen, cyano, carboxyl, sulfonic acid and ester groups, we preferably employ those in which each of R and R. represents an ortho arylene radical. Amongst the compounds of our invention, we have found the following to be particularly effective for our purpose:

Salicylal o-aminophenol 2-hydroxy-3-methoxybenzal o-aminophenol 2-hydroxy-5-methoxybenzal o-aminophenol 2-hydroxy-3-nitrobenzal o-aminophenol 2-salicylalamino-4-aminophenol disalicylal 2,4-

diaminophenol Z-hydroxy-5-ter.-butylbenzal o-aminophenol Z-hydroxy-l-naphthal o-aminophenol Definite operative concentrations of the metal deactivator cannot be specified for each case as the quantity required is dependent upon the amount of metal present in the elastomer. The metal deactivator should be present in the proportion of approximately 3 to times the amount of the metal present, in order to obtain complete deactivation. Higher proportions of metal deactivator may be employed, particularly when a reservoir of metal is present in theform of metal in bulk. Generally from about 0.5% to about 1%, based on the weight of the elastomer, will be suflicient for most purposes.

The catalytically active metal and its compounds may be dissolved in the elastomer or dispersed therein or may be in the form of metal in bulk in intimate contact with the elastomer. It will be understood that. when we refer to an elastomer containing a catalyst, we mean to include those cases wherein the metal in bulk form is in contact with the elastomer, as well as those cases wherein the catalytically active metal is dissolved and dispersed in the elastomer.

The magnitude of the catalytic effect is dependent upon the chemical form of the copper as well as upon its concentration or the area of contact. The following substances were found to have readily measurable pro-oxidant efl'ect: cupric chloride and oleate, metallic copper, cuprous and cupric oxides and cupric sulfide. Even Babbitt metal and aluminum alloys, containing copper, decrease the induction period of gasoline.

Copper is one of the most potent catalysts for the oxidation of many organic products. It is the most powerful and one of the commonest metal contaminants. Other metals, however, diiferent degrees of catalytic activity. Cobalt is quite active, but it seldom occurs in elastomers. Iron is abundant but it is a feeble catalyst. Manganese is definitely harmful, but nickel is practically inert.

It might be casually assumed that, if a metal deactlvator suppresses the activity of one metal, it should do the same for all similar metals, or metals possessing similar catalytic effects. Experiments have proven this assumption to be erroneous. For example, salicylal o-aminophenol deactivates copper, cobalt and iron, but actually increases the catalytic potency of manganese and nickel. The eflect on nickel is interesting since it makes an inert substance catalytically active. It is readily seen that generalizations with respect to different metals are likely to lead to error. The only safe course is to experimentally determine the effects of deactivators on the metals and not to depend upon deductions.

It might be assumed further that, since the condensation products of ortho-hydroxy aromatic aldehydes with ortho-hydroxy aromatic primary amines are metal deactivators, the condensation products of all aromatic aldehydes with all aromatic primary amines are also metal deactivators. It has been experimentally established that this is not the case. All the compounds of this type, which are effective deactivators, contain an ortho-hydroxyl group in each ring, that is, they have at least two hydroxyl groups and in the proper positions. For example, salicylal p-aminophenetole, sallcylal aniline, ptolual o-aminophenol, salicylal m-aminophenol, salicylal p-aminophenol, salicylal o-aminoanisole and di-(p-tolual) 2-4-di-aminophenol are not effective metal deactivators.

It will he observed that the lack of a hydroxyl group in the correct position, the placing of a hydroxyl in a wrong position or blocking a hydroxyl group in the correct position by conversion to an ether renders the compounds so slightly effective that they cannot be classed together with the compounds covered by this invention,

Salicylal p-aminophenol appears to have considerable effect, but the condensation products of p-aminophenol with aldehydes are well recognlzed gasoline antioxidants. Where salicylal p-aminophenol is tested at much lower concentrations, the effect is shown to be practically negli ible.

It has long been recognized that small traces of copper have a very pronounced catalytic effect on the oxidation of eiastomers, such as rubber.

In order to overcome this diiilculty. it has been necessary to establish risorous specifications for the copper content of compounding agents used in rubber. In many cases. particularly with dyes,

- 6 bility. as do sulionie and carbonyl radicals. Unlike the antioxidants the metal deactivators.

are resistant to the action 01 molecular oxygen. and solutions of the deactivators may be kept the removal of traces of copper is both troubleii in P without any mm and parent change. They are thermnly stable but In general, the common antioxidants usedin are destroyed by strong mine-m1 N m unable to suppress um catalytic The deactivators may be added to the clastomer to be protected in any term and manner. tion or copper. The metal deactivators, however.

0 They may be in solid or liquid form, mixed with have been found to be very eflective for this pur other addition agents or dissolved in a solvent. pose. The bomb Physical test was empl yed as a Th ey may be added to the finished products or 1118M evaluating mmmunds- The at any stage in the process for their manufaclowins stock was used in these tests: tum.

15. If the metal deactivators are sumciently sollzfie ble in the elastomer and the conditions are not c e 3 destructive, they will suppress the catalytic ac- Bll fm' tivity of the metals present. They are operative, Btearic acid 1 therefore, in any elastomer, natural or syn- Lithopone 2o thetic. whose rate oi deterioration is accelerm. .e 1 1 guanidine 0- 5 ated by copper, cobalt or iron. The deaetivators Phenyl-beta-naphthylamine (antioxidant) 1.0 also function in solutions of these substances in copper as stearate x solvents as well as in mixtures. n w deantivator 0.5 xtu es of metal deactivators may be used, as well as the condensation products or a given Cured for min. at 40 pound steam pressure. amine with a mixture of aldehydes or a given 'Issu The efl'ect of metal deactivators in rubber containing copper and an antioxidant Cmmmo Cu consggmm omw g 0.5% lwfivgl: 0.5% cons oi om z, oow c om, Daysst70C.&iml0; I

Tum PerEl' J'ent Tum Per gont Tens. Perni'llent Tens. Permillcnt Tum Per ii lent Tum Permgent 8,660 sen sow 3.71s can 2,000 can 2,025 2.500 an 2.110 am not 1,125 000 2,075 sso 2,100 1,525 an is s: it: s iaw mo r137 13m m #3??? 1:13;: 3:3

li o-aminophenoi.

It will be seen from this table that the antioxidant, phenyl-beta-naphthylamine, is unable to deactivate copper. On the other hand, the two deactivators are about equally effective and overcome practically all the catalytic action of the added copper.

The metal deactivators, belonging to the particular class of this invention, are easily prepared by reacting one mol of aldehyde with one moi ot amine with or without the use of a suitable solvent, such as water, methanol, ethanol, pyridine or benzene. The reactions are exothermic and water is formed. Nearly theoretical yields 01 the compounds are obtained. The chemical equation for the formation of saiioyial o-aminophenoLSOAJs:

Their solubility in elastomers is dependent upon their constitution. For example, the ring alkylated compounds tend to be more soluble than those without hydrocarbon ring substituents. Additional hydroxyl groups decrease solualdehyde with a mixture 01- amines. Besides many others, the compounds, obtained condensing each of the following aldehydes with cats): of the following amines are metal deactiva rs:

Aidehydes Amines 2-hydroxybenzaidehyde fl-amin henol z-hydroxy-b-chhirobenraldeh do il-amin -t-methylphenol 2,amino+nitrophsnol 2-hydroxy-3,5-dibromoben dehyde I 2-hydroxy-3-nitrobensaldehydc 2-hydroxy-6-methylbensaldeh do Z-hydrox -3-Inethor benseide yde nml dehyde fl-hydroxy-a-cyanoben dehyde il-hydroxy-S-oarbox benzaldehyde 2-hydroxybensaide ydei-miionlo S-aminoA-hydroryquinoline wane uydrorypyridine-aldeb auaaoo bodiments disclosed in the examples, but we intend to cover our invention broadly as in the appended claims.

This application is a division of our application Serial No. 412,602, filed September 27, 1941, and now Patent No. 2,426,766, issued September 2, 1947.

We claim:

1. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of copper, cobalt, iron and their compounds, normally effective to catalyze oxidation 01' said rubber, and having incorporated therein a metal deactivator in a small proportion suiflcient to deactivate said catalyst, said metal deactivator having the formula HORF-CH=N--R'--OH wherein each of R and R represents an ortho arylene radical.

2. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of copper, cobalt, iron and their compounds, normally effective to catalyze oxidation of said rubber, a small amount of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less eflective in the presence oi said catalyst. and having incorporated therein a metal deactivator in a small proportion sufflcient to deactivate said catalyst, said metal deactivator having the formula wherein each of R andR represents an ortho divalent aromatic radical.

3. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of copper, cobalt, iron and their compounds, normally eflective to catalyze oxidation of said rubber, a small amount of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less eflective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator having the formula wherein each of R and R represents an ortho arylene radical.

4. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst or the group consisting of copper, cobalt, iron and their compounds, normally efl'ective to catalyze oxidation of said rubber, a small amount of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less effective in the presence of said catalyst, and having incorporated therein a. metal deactivator in a small proportion sufflcient to deactivate said catalyst, said metal deactivator having the formula no-a-cH=N-n'-on wherein each of R and R represents an ortho divalent mononuclear aromatic radical oi the benzene series.

5. A composition comprising rubber, normally subject to deterioration caused by the action of molecular'oxygen, containing a. catalyst of the group consisting of copper, cobalt, iron and their compounds, normally effective to catalyze oxidation of said rubber, a small amount of an antioxidant, normally eiiective to materially retard such deterioration in the absence of said catalyst but which is less eiiective in the presence or said catalyst, and having incorporated therein a, metal deactivator in a small proportion sufflcient to deactivate said catalyst, said metal deactivator having the formula wherein each of R and R represents an ortho mononuclear arylene radical of the benzene series.

6. A composition comprising rubber, normally subject to deterioration caused by the action oi! molecular oxygen, containing a catalyst 01' the group consisting of copper, cobalt, iron and their compounds, normally eflective to catalyze oxidation of said rubber, a small amount or an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less effective in the presence oi. said catalyst, and having incorporated therein a metal deactivator in a small proportion suiiiclent to deactivate said catalyst. said metal deactivator being salicylal o-aminophenol.

7. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst 01' the group consisting of copper, cobalt, iron and their compounds, normally eflective to catalyze oxidation of said rubber, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator having the formula wherein each of R and R represents an ortho divalent aromatic radical.

8. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of copper, cobalt, iron and their compounds, normally effective to catalyze oxidation of said rubber, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator having the formula wherein each of R and R represents an ortho divalent mononuclear aromatic radical of the benzene series.

9. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of copper, cobalt, iron and their compounds, normally eflective to catalyze oxidation of said rubber, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator having the formula wherein each of R and R represents an ortho mononuclear arylene radical of the benzene series.

10. A composition comprising rubber, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst 01' the group consisting of copper, cobalt, iron and their compounds, normally effective to catalyze oxidation of said rubber, and having incorporated therein a metal deactivator in a small propor- 9 tion suillcient to deactivate said catalyst, said metal deactivator being salicylal o-arninophenol.

11. The method of inhibiting the catalytic oxidation of rubber caused by a catalyst of the group consisting of copper, cobalt, iron and their compounds which comprises incorporating in said rubber a small amount, sufllcient to deactivate said catalyst. of a. metal deactivator having the formula HORCH=N-R'-OH wherein each of R and R represents an ortho divalent aromatic radical.

12. The method of inhibiting the catalytic oxidation of rubber caused by a catalyst of the group consisting of copper, cobalt, iron and their comounds which comprises incorporating in said rubber a small amount, suiiicient to deactivate said catalyst, of a metal deactivator having the formula HO-R-CH=NR'OH wherein each or R and It represents an ortho 10 divalent mononuclear aromatic radical of the benzene series.

13. The method or inhibiting the catalytic oxidation of rubber caused by a catalyst or the group consisting of copper. cobalt, iron and their compounds which comprises incorporating in said rubber a small amount, suflicient to deactivate said catalyst, of a metal deactivator, said metal deactivator being salicylal o-aminophenol.

FREDERICK B. DOWNING.

CHARLES J. PEDERSEN.

REFERENCES CITED The following reierences are of record in the Certificate of Correction Patent No. 2,442,200.

file of this patent:

UNITED STATES PATENTS Number Name Date 2,249,802 Chenicek July 15. 1941 2,300,998 White Nov. 3, 1942 May 25, 1948.

FREDERICK B. DOWNING ET AL. It is hereby certified that error appears in the grinted specification of the above numbered patent requiring correction as follows:

olumn 1, line 23, for the word monoxides read molomkies; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 3rd day of August, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommiesioner of Patents.

9 tion suillcient to deactivate said catalyst, said metal deactivator being salicylal o-arninophenol.

11. The method of inhibiting the catalytic oxidation of rubber caused by a catalyst of the group consisting of copper, cobalt, iron and their compounds which comprises incorporating in said rubber a small amount, sufllcient to deactivate said catalyst. of a. metal deactivator having the formula HORCH=N-R'-OH wherein each of R and R represents an ortho divalent aromatic radical.

12. The method of inhibiting the catalytic oxidation of rubber caused by a catalyst of the group consisting of copper, cobalt, iron and their comounds which comprises incorporating in said rubber a small amount, suiiicient to deactivate said catalyst, of a metal deactivator having the formula HO-R-CH=NR'OH wherein each or R and It represents an ortho 10 divalent mononuclear aromatic radical of the benzene series.

13. The method or inhibiting the catalytic oxidation of rubber caused by a catalyst or the group consisting of copper. cobalt, iron and their compounds which comprises incorporating in said rubber a small amount, suflicient to deactivate said catalyst, of a metal deactivator, said metal deactivator being salicylal o-aminophenol.

FREDERICK B. DOWNING.

CHARLES J. PEDERSEN.

REFERENCES CITED The following reierences are of record in the Certificate of Correction Patent No. 2,442,200.

file of this patent:

UNITED STATES PATENTS Number Name Date 2,249,802 Chenicek July 15. 1941 2,300,998 White Nov. 3, 1942 May 25, 1948.

FREDERICK B. DOWNING ET AL. It is hereby certified that error appears in the grinted specification of the above numbered patent requiring correction as follows:

olumn 1, line 23, for the word monoxides read molomkies; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 3rd day of August, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommiesioner of Patents. 

